The present invention is generally directed to an improved creping adhesive. More particularly, the present invention is directed to a creping adhesive used in print and crepe operations for producing wipers and other liquid absorbent products.
Liquid absorbent products such as paper towels, tissue paper, feminine hygiene products, industrial wipers, food service wipers, napkins, medical pads, and other similar products are designed to include several important properties. For example, the products should generally have good bulk, a soft feel and should be highly absorbent. Depending on the application, the products should also have good strength even when wet and should resist tearing. Further, many products should also have good stretch characteristics, should be abrasion resistant, and should not deteriorate in the environment in which they are used.
One particular process that has proven to be very successful in producing paper towels and other wiping products is disclosed in U.S. Pat. No. 3,879,257 to Gentile, et al., which is incorporated herein by reference in its entirety. In Gentile. et al., a process is disclosed for producing soft, absorbent, single ply fibrous webs having a laminate-like structure that are particularly well suited for use as wiping products.
The fibrous webs disclosed in Gentile, et al. are formed from an aqueous slurry of principally lignocellulosic fibers under conditions which reduce inner fiber bonding. A bonding material, such as a latex elastomeric composition, is applied to a first surface of the web in a spaced-apart pattern. In particular, the bonding material is applied so that it covers from about 50% to about 60% of the surface area of the web. The bonding material provides strength to the web and abrasion resistance to the surface. Once applied, the bonding material can penetrate the web preferably from about 10% to about 40% of the thickness of the web.
The bonding material can then be similarly applied to the opposite side of the web for further providing additional strength and abrasion resistance. Once the bonding material is applied to the second side of the web, the web can be brought into contact with a creping surface. Specifically, the web will adhere to the creping surface according to the pattern to which the bonding material was applied. The web is then creped from the creping surface with a doctor blade. Creping the web greatly disrupts the fibers within the web, thereby increasing the softness, absorbency, and bulk of the web.
In one of the preferred embodiments disclosed in Gentile, et al., both sides of the paper web are creped after the bonding material has been applied. Gentile, et al. also discusses the use of chemical debonders to treat the fibers prior to forming the web in order to further reduce innerfiber bonding and to increase softness and bulk.
Although the processes disclosed in Gentile, et al. have provided great advancements in the art of making disposable wiping products, the present invention is directed to further improvements in nonwoven fibrous base webs. In particular, the present invention is directed to a fibrous base web incorporating an improved bonding material or creping adhesive that is used during creping the base web. The creping adhesive of the present invention is not only economical to produce in comparison to conventional materials, but also has improved adhesive strength, has improved solvent resistance, and improves latex efficiency.
As stated above, the present invention is directed to further improvements in prior art constructions and methods, which are achieved by providing a nonwoven base web made from pulp fibers, synthetic fibers, and/or other various fibers. A bonding material is applied to at least one side of the base web. In particular, the bonding material may be applied to the web according to a predetermined pattern, such as a geometric pattern. In accordance with the present invention, the bonding material applied to the web contains a mixture of an adhesive and composite particles. In general, the adhesive can be any conventionally used print creping adhesive such as an acrylate, a vinyl acetate, a vinyl chloride, or a methacrylate. In one embodiment, the adhesive can be cross-linkable in order to make the resulting product water resistant. Cross-linkable adhesives include styrene butadiene such as carboxylated styrene butadiene or an ethylene vinyl acetate copolymer. For example, the ethylene vinyl acetate copolymer can be cross-linked with N-methyl acrylamide groups.
The composite particles combined with the adhesive, on the other hand, comprises ultrafine particles. The composite particles can be present in the bonding material generally in an amount up to about 30% by weight and particularly from about 10% to about 30% by weight. According to the present invention, the composite particles can have a median particle size of less than about 5 microns, particularly less than about 1 micron, and more particularly less than about 0.5 microns. The composite particles can have a particle size distribution of less than about 10 microns, particularly less than about 5 microns, and more particularly less than about 1 micron.
The composite particles used in the present invention can generally be made from any material that does not completely dissolve in the adhesive, does not damage the base web, or does not have an adverse impact on the adhesive. For example, the composite particles can be made from clays, titanium dioxide, talc, zeolite, silica, calcium carbonate, or mixtures thereof. In one embodiment, the composite particles are obtained from kaolin clay.
When present in the bonding material, it has been discovered that the composite particles increase the adhesive strength of the adhesive without adversely interfering with the other properties of the adhesive. In fact, the composite particles improve the efficiency of the adhesive, meaning that less adhesive can be used in forming products in accordance with the present invention.
The bonding material applied to the base web can be applied in a pattern that covers from about 10% to about 60%, and more particularly from about 20% to about 50% of the surface area of each side of the web. The bonding material can be applied to each side of the web in an amount up to about 10% by weight, and particularly from about 2% to about 8% by weight. Once applied, the bonding material can penetrate the web in an amount from about 10% to about 60% of the total thickness of the web, and particularly from about 15% to about 40% of the thickness.
The preselected pattern used to apply the bonding material can be, in one embodiment, a reticular interconnected design. Alternatively, the preselected pattern can comprise a succession of discrete shapes, such as dots. In a further alternative embodiment of the present invention, the preselected pattern can be a combination of a reticular interconnected design and a succession of discrete shapes.
Once formed, the base web of the present invention can have any suitable basis weight such as from about 20 pounds per ream to about 80 pounds per ream, depending upon the particular application. The base web can be used in numerous products. For instance, the base web can be used as a wiping product, as a napkin, as a tissue paper, as a feminine hygiene product, as a medical pad, as a placemat, as a cover material such as a car cover, as a paint drop cloth, as one layer in a laminate product or as any other similar liquid absorbent product or filter product.
Alternatively, the present invention is directed to a creping adhesive composition for adhering a base web to a creping surface. The creping adhesive composition contains an adhesive, such as an acrylate, a vinyl acetate, a vinyl chloride, a methacrylate or a styrene butadiene. In one embodiment, for instance, the adhesive can be a cross-linked latex, such as a cross-linked ethylene vinyl acetate copolymer.
In accordance with the present invention, the creping adhesive composition further contains composite particles as described above. For instance, the composite particles can have a median particle size of less than about 1 micron and a particle size distribution wherein 90% of the composite particles have a size less than about 5 microns. The composite particles can be present in the composition in an amount up to about 30% by weight.
Once applied to a base web, it has been discovered that the creping adhesive composition of the present invention has an adhesive strength equivalent to or better than a creping adhesive composition applied to a base web in the same amount that contains the adhesive but not the composite particles.
The composite particles can be, for instance, clay, titanium dioxide, talc, zeolite, silica, and mixtures thereof. In one embodiment, kaolin clay is used. The kaolin clay can have a median particle size of less than about 0.5 microns and can have a particle size distribution wherein 90% of the particles have a particle size less than about 1 micron.
Other features and aspects of the present invention are discussed in greater detail below.